The Education Ministry Key Lab of Resource Chemistry, and Department of Chemistry, Shanghai Normal University, Shanghai 200234, P. R. China.
J Am Chem Soc. 2013 Aug 14;135(32):11849-60. doi: 10.1021/ja403822d. Epub 2013 Aug 2.
A coordination-assisted synthetic approach is reported here for the synthesis of highly active and stable gold nanoparticle catalysts in ordered mesoporous carbon materials using triblock copolymer F127 as a structure-directing agent, thiol-containing silane as a coordination agent, HAuCl4 as a gold source, and phenolic resin as a carbon source. Upon carbonization, the gold precursor becomes reduced to form monodispersed Au nanoparticles of ca. 9.0 nm, which are entrapped or confined by the "rigid" mesoporous carbonaceous framework. Nanoparticle aggregation is inhibited even at a high temperature of 600 °C. After removal of the silica component, the materials possess the ordered mesostructure, high surface area (1800 m(2)/g), large pore volume (1.19 cm(3)/g), and uniform bimodal mesopore size (<2.0 and 4.0 nm). The monodispersed gold nanoparticles are highly exposed because of the interpenetrated bimodal pores in the carbon framework, which exhibit excellent catalytic performance. A completely selective conversion of benzyl alcohol in water to benzoic acid can be achieved at 90 °C and 1 MPa oxygen. Benzyl alcohol can also be quantitatively converted to benzoic acid at 60 °C even under an atmospheric pressure, showing great advantages in green chemistry. The catalysts are stable, poison resistant, and reusable with little activity loss due to metal leaching. The silane coupling agent played several functions in this approach: (1) coordinating with gold species by the thiol group to benefit formation of monodispersed Au nanoparticles; (2) reacting with phenolic resins by silanol groups to form relatively "rigid" composite framework; (3) pore-forming agent to generate secondary pores in carbon pore walls, which lead to higher surface area, larger pore volumes, and higher accessibility to to the gold nanoparticles. Complete removal of the silica component proves to have little effect on the catalytic performance of entrapped Au nanoparticles.
本文报道了一种协同合成策略，用于在有序介孔碳材料中合成高活性和稳定的金纳米粒子催化剂。该策略使用三嵌段共聚物 F127 作为结构导向剂、含硫醇的硅烷作为配位剂、HAuCl4 作为金源、酚醛树脂作为碳源。碳化后，金前驱体被还原形成约 9.0nm 的单分散 Au 纳米粒子，这些纳米粒子被“刚性”介孔碳质骨架包埋或限制。即使在 600°C 的高温下，纳米粒子的聚集也受到抑制。除去硅组分后，材料具有有序的介孔结构、高比表面积（1800m2/g）、大孔体积（1.19cm3/g）和均匀的双模态介孔尺寸（<2.0 和 4.0nm）。由于碳骨架中互穿的双模态孔，单分散的金纳米粒子高度暴露，表现出优异的催化性能。在 90°C 和 1MPa 氧气下，苯甲醇在水中可完全选择性转化为苯甲酸。即使在常压下，苯甲醇也能定量转化为苯甲酸，在绿色化学方面具有很大的优势。该催化剂具有稳定性、抗中毒性和可重复使用性，由于金属浸出，活性损失很小。硅烷偶联剂在该方法中发挥了多种作用：（1）通过巯基与金物种配位，有利于形成单分散的 Au 纳米粒子；（2）通过硅醇基与酚醛树脂反应，形成相对“刚性”的复合骨架；（3）作为造孔剂，在碳孔壁中生成次级孔，从而提高比表面积、孔体积和金纳米粒子的可及性。完全除去硅组分对被包埋的 Au 纳米粒子的催化性能几乎没有影响。
